Swfit 枚举

枚举为一组相关值定义了一个通用类型，从而可以让你在代码中类型安全地操作这些值。

基本用法

enum RequestType{
    case get
    case post
    case put
    case delete
}

原始值(Raw Values)

// 原始值,  不写默认是枚举值
enum Grade: String {
    case perfect = "A"
    case great = "B"
    case good = "C"
    case bad = "D"
}
print(Grade.perfect)   // perfect
print(Grade.perfect.rawValue)   // A 

如果枚举的原始值类型是Int、String，Swift会自动分配原始值

enum Season : Int {
    case spring, summer, autumn, winter
}
print(Season.spring.rawValue)    // 0
print(Season.summer.rawValue) // 1
print(Season.autumn.rawValue)  // 2
print(Season.winter.rawValue)    // 3

关联值

将枚举的成员值 跟其他类型的关联存储在一起，有时会非常有用。

enum Date {
    case digit(year: Int, month: Int, day: Int)
    case string(String)
}
var date = Date.digit(year: 2011, month: 9, day: 10)
date = .string("2011-09-10")
switch date {
case .digit(let year, let month, let day):
    print(year, month, day)
case let .string(value):      // ? ? ?
    print(value)
}

递归枚举

枚举值包含自己枚举，需要使用indirect关键字

indirect enum ArithExpr {
case number(Int)
case sum(ArithExpr, ArithExpr)
case difference(ArithExpr, ArithExpr)
}

let five = ArithExpr.number(5)
let four = ArithExpr.number(4)
let two = ArithExpr.number(2)
let sum = ArithExpr.sum(five, four)
let difference = ArithExpr.difference(sum, two) 

可以使用MemoryLayout获取数据类型占用的内存大小

 enum Password {
    case number(Int, Int, Int, Int)
    case other
}

MemoryLayout<Password>.stride // 40, 分配占用的空间大小 
MemoryLayout<Password>.size // 33, 实际用到的空间大小 
MemoryLayout<Password>.alignment // 8, 对齐参数